This invention relates to portable testing apparatus for a circuit breaker and, in particular, to testing apparatus for use in testing residential circuit breaker panels.
Small business establishments and residences have their electric service brought to an external panel which contains a main circuit breaker and a number of individual low current circuit breakers. The breakers are rated by testing agencies to provide an open circuit under certain conditions. The primary circuit breaker that is actuated when the total current demand within the residence exceeds the rating will be actuated under limited circumstances. This circuit breaker is in series with a number of individual circuit breakers that define the current limitations of the individual circuits in the place of service. Most residential panels have 12 individual circuit breakers each rated at up to 60 amps.
The circuit breaker panels of residences are usually located on the exterior of the house at a point proximate to the distribution network of the utility. The placement is designed to shorten the distance to the distribution feeder and to provide a measure of safety in its location. Consequently, it is normally not proximate to the area of the residence that it controls. In order to conduct a test of an individual circuit breaker, it is heretofore common for an electrician to intentionally promote a short circuit within the dwelling and then make the trip out to the panel to determine which breaker was actuated. In the case where there is no immediate reaction to an intentional short circuit, it is frequently necessary to determine by a process of elimination which circuit breaker failed to open upon the creation of the intentional short within the dwelling. This is a time consuming and roundabout method of testing individual circuit breakers.
While the electrician servicing a small business establishment or residence can take the time to create short circuits at each of the circuits in the house, he may be duplicating his testing if he is not provided with a schematic at the time. However, a second test of breaker function is recommended and rarely, if ever, performed on low current breakers. This is the constant current test. Circuit breakers are designed to open when the amount of current remains constant on a particular circuit for a period of time. This constant load test is normally not performed in reviewing existing residential electric service.
The failure of an individual circuit breaker to open under short circuit conditions has serious consequences. In many residences and small business establishments, a master or primary circuit breaker is connected in series with the individual low current breakers to provide safety through redundancy. If an individual circuit breaker fails to open, it is quite likely that the high current flow will cause the master breaker, if present, to open promptly. However, the inability of the circuit breaker to maintain rated performance under overload conditions can be much more serious since the current flow through the electrical circuit served by this breaker may not exceed the rated current of the master breaker. In this case, the secondary breaker may not open at the appropriate current level. During the time that the individual circuit is experiencing this overload condition, the wires that form the circuit are drawing an abnormally large current and may be heating to an unsafe condition within a wall or otherwise out of view. Thus, the overlooking of the performance of a constant load test for individual circuit breakers is potentially hazardous.
The homeowners responsibility for the electric service begins at the electric meter provided by the utility. Consequently, the interest in the utility in providing apparatus for testing individual circuit breakers is limited with their attention being primarily directed to their own equipment. The manufacturers of apparatus used for transmission and distribution of electricity on a wholesale basis have expended substantial time and energy in providing a variety of different methods of automatically testing the operation of large capacity circuit breakers. This technology has not provided a relatively portable apparatus that is available for the electrician servicing the low current equipment at an individual residence.
Accordingly, the present invention is directed to the provision of a portable testing apparatus for circuit breakers. In particular, the apparatus is directed to the testing of circuit breakers used in residential and small business establishment panels. Further, the present invention is directed to the provision of a portable apparatus in which the operator can perform both a short circuit test and a constant load test.